The present invention relates to an electric blower suitable for use in a vacuum cleaner.
A prior art electric blower of the type described above has been so constructed that, as shown in FIG. 13, an impeller 2 and an air guide 3 are provided in a casing 1, and the impeller 2 is rotated at a high speed by a motor 4 to thereby provide a required air flow rate as well as a vacuum pressure.
In such an electric blower as described above wherein the air guide 3 is disposed around the outer periphery of the impeller 2, problem of noise arises which is thought to be generated due to the fact that the air flow discharged from the impeller 2 impinges against the inlet of the air guide 3, when it flows into the air guide. The most significant factor for generating the noise is in the range of frequences of sound resulting from the product of the number Z of blades and the number N of rotations of the impeller 2, which are referred to in general as NZ sound, FIG. 12 shows the NZ sound.